The present invention relates to capacitive membrane ultrasonic transducers (CMUTs). In particular, electrical interconnections are provided for CMUTs.
CMUTs typically have a void covered by a membrane. An electrode is positioned on the membrane and another at the base of the void. To generate acoustic energy, an electrically varying signal is applied to one of the electrodes, causing the membrane to flex. To generate electrical energy, the acoustically induced flexing of the membrane generates a differential electrical signal between the two electrodes.
A typical 1D or 2D ultrasound transducer includes hundreds or even thousands of separate transducer elements, each requiring separate signal paths. For a CMUT, a plurality of membranes and associated electrodes may be used together to form a single element. For interconnecting the electrodes for each element to a separate imaging system signal path, a conductor is deposited on a top surface of the CMUT. The electrode in the void may be connected through a via to a conductor on the top surface. The signal traces are then routed or patterned to an edge of the top surface of the CMUT. Wire bonds or flex circuits connect with pads along the edge to complete the interconnection with the imaging system. However, as the density or number of elements increases, such as in a two-dimensional transducer array, the available space for routing electrically isolated traces on a top surface of the CMUT may not be sufficient.
Transistors and other semiconductor devices may be integrated with a CMUT. The integrated electronics are provided below the CMUT, such as in a same semiconductor substrate or a different semiconductor substrate bonded to the CMUT. For electrical interconnection with the electronics, vias are provided from the electrodes of the CMUT through the silicon substrate. To protect digital and analog components, a grounding plane may be formed within the substrate between the CMUT devices and the electronics. U.S. Published Application 2003/0032211 shows one such grounding plane. The grounding plane is patterned to avoid connection with the vias of the electrodes from the CMUT. However, integration of electronics devices and the associated vias for electrical interconnection may add complication to manufacturing, especially where lower cost transducers are desired.